Fatigue and Fracture Committee Approves New Standard on Resistance to Stable Crack Extension

Many structures, such as aircraft or other lightweight vehicles, are made from thin-ductile structural materials that exhibit low crack-front constraint, which allows for extensive plastic yielding of the material around a crack front. However, many current standards, such as E 399, Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic Materials, or E 1820, Test Method for Measurement of Fracture Toughness, were developed for thick-brittle materials, under plane-strain conditions, or thick-ductile materials under high constraint conditions around the crack front.

ASTM International Committee E08 on Fatigue and Fracture has now developed a standard that can be used for thin-ductile structural materials. The standard, E 2472, Test Method for Determination of Resistance to Stable Crack Extension Under Low Constraint Conditions, is under the jurisdiction of Subcommittee E08.07 on Linear-Elastic Fracture. While the new standard is similar to E 1820 in that it has its foundation in non-linear fracture mechanics, it differs from other fracture standards because it is based on a parameter that can be directly measured on the fracture specimen and/or structural component.

According to James Newman, professor, department of aerospace engineering, Mississippi State University, E 2472 will be useful primarily in the aerospace and piping industries, though it will applicable for any thin-ductile tension loaded structures.

Newman says that the subcommittee is actively seeking participation, particularly from the aerospace and piping industry, to increase the application of the new standard to predicting structural behavior of cracked components. “The use and application of the new standard will require more expertise in testing and analysis,” says Newman. “The testing setup and equipment required is more complex, but many state-of-the-art testing laboratories should have these capabilities.” //